WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2016 21 Two- and three-year growing of whitefish is carried out in lakes with a favorable winter oxygen regime. In this case, the size of whitefish reaches 300 g after the second year and 600 g after the third year. If a lake has an existing fish community, one of the major conditions for successful growing is the use of relatively large-size stocking material. Usually such lakes are stocked with fingerlings that are grown in special lake-nurseries. In some cases, aeration equipment is installed in lakes to ensure suitable conditions for overwintering. However, such intensification measures significantly increase the cost of the resulting fish products. Therefore, ponds with two or three-year production cycles account for less than 10 percent of C. peled and its hybrids. In addition to C. peled, large forms of European vendace C. albula ladogensis and C. lavaretus maraenoides have been grown in small and medium size, relatively deep man-made lakes of the Urals for over 50 years. As objects of aquaculture, these whitefish were brought to the Urals from Ladoga and Peipus Lakes in the 1930s. In 2015, 147 t of C. albula ladogensis and 5 t of C. lavaretus maraenoides were harvested. Given the area of suitable lakes, the scope of extensive aquaculture of whitefish in the south of Western Siberia and the Urals can be increased to 21,000 t. However, implementation of these plans is constrained by a number of legal and organizational problems. Whitefish Hatcheries Artificial reproduction and extensive lake fish farming increase the demand for larvae. The main producer of whitefish larvae in the region is Tobolsk Regional Fish Farm (Tobolsk) which is a branch of concentration of zooplankton is 2-10 g/L. Usually whitefish larvae are stocked at 1-5 days of age at 3-5 mg in weight and 7-9 mm in length. Sometimes larvae are grown for 5-10 days in hatchery tanks and fed with Artemia nauplii before being stocked in lakes. The stocking density of larvae in lakes is 1,000-4,000/ha. Whitefish reach an average weight of about 100 g (Fig. 4) during the first growing season (May to October) and then are captured for processing and marketing. Fingerlings of hybrid C. peled and C. nasus are 30-40 percent larger in weight than C. peled. Therefore there is more demand for stocking hybrid whitefish; as many as 200 million hybrid larvae are sold annually. A 30-y statistical analysis has shown that the average stocking of 1 million larvae provides a harvest of 11 t of commodity C. peled fingerlings. The maximum value of this indicator reached 70 t from 1 million larvae. On average, the seasonal catch of first-year whitefish is 26 kg/ha, with a maximum of 114 kg/ha, providing a commercial return of 13 percent. In the most successful cases, commercial returns reach 50 percent. This form of extensive aquaculture is highly remunerative in these lakes. Commodity whitefish fingerlings are grown in lakes because of the availability of natural food resources. In this regard, buying whitefish larvae for stocking lakes and harvesting market-size fish are the main expenses of a fish farmer. First-year whitefish are processed into salted, dried or smoked forms that are considered to be a delicacy. Thus, there is a large consumer demand for these products at all times. The main risk of production failure is connected with excessive summer warming of lakes in some years. In this case, complete mortality of fish in small lakes may occur. In addition, a large number of fish-eating birds, especially cormorant Phalacrocorax carbo, significantly reduces the effectiveness of growing whitefish in lakes, as well as poaching. Whitefish fisheries are also adversely affected by the uncontrolled dispersal of fish species such as Perccocottus glenii from the Far East and Leucaspius delineates from the European part of Russia. These alien fish species have a high tolerance for oxygen deficiency in winter and spring and represent a serious threat to whitefish larvae. In addition, they reduce the share of food resources potentially suitable for the consumption by whitefish. The most damaging parasitic disease of whitefish grown in lakes is caused by trematode larvae of the genus Diplostomum. (CONTINUED ON PAGE 22) FIGURE 3. A larva of Coregonus muksun (left). The larvae of C. muksun feeding on Artemia nauplii (right). FIGURE 4. A one-year old, 100-g Coregonus peled.
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